1. Field
Example embodiments of the following description relate to a median filtering method and apparatus required to remove noise and improve an image quality with respect to all types of input images.
2. Description of the Related Art
An image signal processor requires a higher-level noise removal technology, as a resolution of an image sensor increases and a pixel size decreases. To stably supply improved image processing technologies such as an anti-shake technology, a noise removal technology with an excellent performance and low cost needs to be performed in advance.
A median filter is used to remove noise, together with a mean filter. The median filter provides an excellent subjective image quality, but an operation amount of the median filter is relatively high, compared with the mean filter. When N pieces of data are provided, the mean filter may compute a mean value of the N pieces of data, and accordingly addition may be performed N−1 times and division may be performed once. Assuming that an operation amount required for the division is equal to an operation amount required for the addition, an operation needs to be performed N times. A conventional median filter searches for a minimum value or a maximum value from all of N pieces of data, searches for a minimum value or a maximum value from remaining data again, and searches for a median value by excluding the N pieces of data one by one. When N is an odd number, the mean filter may require an operation in proportion to N, and the median filter may require an operation in proportion to N^2. When the median filter is applied to a two-dimensional (2D) space having an N×N block size, the operation amount may be proportional to N^4. Additionally, when the median filter is applied to a three-dimensional (3D) space, the operation amount may be proportional to N^6. Accordingly, in a multi-dimensional space, the operation amount may be exponentially increased.